<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body,h2,ul,li,form,span{
            margin: 0;
            padding: 0;
            border: 0;
            text-decoration: none;
        }
        #box{
            width: 300px;
            border: 1px solid red;
        }
        h2{
            background: green;
        }
        form{
            background-color: aqua;
        }
        div:nth-of-type(1)>input{
            border: 3px solid black;
        }
        div:nth-of-type(2)>input{
            border: 2px dashed black;
        }
        div:nth-of-type(3)>input{
            border: 3px solid yellow;
        }
    </style>
</head>
<body>

<div id="box">
    <h2>会员登录</h2>
    <form action="#">
        <div>
            <span>用户名：</span>
            <input type="text"></input>
        </div>
        <div>
            <span>密码：</span>
            <input type="text"></input>
        </div>
        <div>
            <span>邮箱：</span>
            <input type="text"></input>
        </div>
    </form>
</div>

</body>
</html>